Brown algae are quite common in

Mannitol is the stored food in $..........$.

The cell wall of algae is composed of which of the following?

Chlorophyll $c$ and $d$ are characteristic pigments of ........ respectively.

Assertion : Red algae contribute to the production of coral reefs.
Reason : Some red algae secrete and deposit calcium carbonate over their walls.

Identify $X$ and $Y$ in the given figure.